1. Field of the Disclosure
The present disclosure relates to a hybrid driving manner Organic Light Emitting Diode (OLED) display apparatus.
2. Description of the Prior Art
An Organic Light Emitting Diode (OLED) display apparatus that has come into the spotlight as a display apparatus has advantages of a fast response rate, high light emitting efficiency, high luminance and a wide viewing angle because of using an OLED which emits light by itself.
FIGS. 1A and 1B are views illustrating a characteristic of a driving transistor driving the OLED in the OLED display apparatus. FIG. 1A illustrates a structure of the driving transistor DT connected to the organic light emitting diode OLED, and FIG. 1B illustrates a saturation curve of a drain-source current Ids of the driving transistor DT.
Referring to FIG. 1A, the driving transistor DT is connected to the organic light emitting diode OLED. The display apparatus controls the drain-source current Ids flowing to the organic light emitting diode OLED by controlling a gate-source voltage Vgs of the driving transistor DT.
At this time, a drain-source voltage Vds should be maintained in a level equal to or higher than a certain level in order to flow the drain-source current Ids to the driving transistor DT, and to this end, a conventional display apparatus inputs a high potential voltage VDD having a certain level to a drain terminal (D) of the driving transistor DT.
Some problems in a case where the conventional display apparatus provides the high potential voltage VDD having the certain level to the driving transistor DT are described with reference to the FIG. 1B.
Referring to FIG. 1B, since the display apparatus drives the driving transistor DT in a saturation region, in order to provide a drain-source current of Ids_a ampere (A) to the OLED, the display apparatus provides Vgs_a volt (V) as the gate-source voltage and also provides the drain-source voltage Vds higher than a drain-source voltage Vds_a of a saturation point Pa1. In the same manner, in order to provide a drain-source current of Ids_b A to the OLED, the display apparatus provides Vgs_b V as the gate-source voltage and also provides the drain-source voltage Vds higher than a drain-source voltage Vds_b of a saturation point Pb1.
The drain-source voltage Vds of the driving transistor DT is determined by the high potential voltage VDD provided to the drain terminal (D) of the driving transistor DT. The conventional display apparatus provides a fixed high potential voltage VDD capable of providing the drain-source voltage equal to or higher than a saturation point in correspondence to a highest drain-source current, in order to provide the drain-source voltage Vds equal to or higher than a certain level in correspondence to all of drain-source currents Ids having several levels.
In FIG. 1B, the highest drain-source current is Ids_a A, and the display apparatus sets the high potential voltage VDD so that the drain-source voltage Vds is higher than the drain-source voltage Vds_a of the saturation point Pa1. The saturation point of the driving transistor DT may be changed according to a characteristic such as a temperature and so on, and thus the display apparatus provides the drain-source voltage in consideration of a certain margin. In FIG. 1B, the display apparatus provides a drain-source voltage Vds_m corresponding to the saturation point Pa2.
Since the high potential voltage VDD is fixed with one level in the conventional display apparatus, when the drain-source voltage is determined as Vds_m V, the display apparatus drives the driving transistor DT at a point Pb2 with respect to the drain-source current.
But, when the display apparatus drives the driving transistor DT at the point Pb2 as described above, power may be excessively dissipated in a corresponding state.
The same levels of drain-source currents Ids are provided to the OLED at the points Pb1 and Pb2, and a drain-source voltage difference is generated between the point Pb2 and the point Pb1. Here, the drain-source voltage difference is Vsur V. Loss of the driving transistor DT is determined by a product of multiplication between the drain-source current Ids and the drain-source voltage Vds as noted from the following equation 1.Loss of driving transistor DT=drain-source current Ids*drain-source voltage Vds  [Equation 1]
According to equation 1, the loss of the driving transistor DT at the point Pb2 is larger than the loss of the driving transistor DT at the point Pb1. Here, the loss difference between the Pb2 and the Pb1 is Ids_b A*Vsur V.
The power dissipated in the driving transistor, firstly, generates a problem of increasing power consumption of the OLED display apparatus. In addition, such a loss generated in the driving transistor DT generates heat, and thus the loss, secondly, generates a problem of shortening life expectancy of the driving transistor DT.
The reason why the conventional display apparatus generates the above-mentioned loss in the driving transistor DT by fixing the high potential voltage VDD is because the conventional display apparatus performs a single frame driving manner. The one high potential voltage VDD is used in one frame, and since the conventional display apparatus drives all pixels in the single frame driving manner, the above-mentioned problems are incurred.